One of the primary goals in designing mobile telephones is to reduce power consumption in order to increase battery-life. In large part, the power consumption of a mobile telephone is dependent upon the amount of current drawn by a power amplifier in the transmit chain that operates to amplify a transmit signal prior to sending the signal to the antenna for transmission. In general, the power amplifier is designed to operate based on an ideal load at the antenna. However, due to factors such as how a user is holding the phone and the distance between the antenna and the user's body, the load seen by the power amplifier varies. Thus, a mismatch is created between the power amplifier and the antenna. For example, the power amplifier may be designed to operate with an ideal load of 50 ohms. However, a user may hold a phone such that the load seen at the antenna is 25 ohms, thereby creating a 2:1 mismatch. This mismatch can be as large as 10:1 and causes a large amount of current to flow through the power amplifier, thereby reducing the battery-life of the mobile telephone. Accordingly, there remains a need for a system that limits the current in the power amplifier in order to prevent large amounts of current from flowing through the power amplifier due to load mismatch.
A system that limits current in the power amplifier must detect the current in the power amplifier. Thus, there remains a need for current detection circuitry that detects the current in the power amplifier and that does not substantially affect the efficiency of the power amplifier.